PROJECT SUMMARY Many forms of human dementia are caused by aberrantly folded proteins and protein aggregates. Overexpressing these disease proteins, such as ?-synuclein and TBD-43, in the budding yeast Saccharomyces cerevisiae, also causes cytotoxicity, allowing unbiased powerful genetic screens for modifiers that enhance or repress toxicity. Hence, this single-celled eukaryotic model has been a powerful genetic tool for discovering molecular pathways regulating human dementia caused by protein misfolding and aggregation, such as the Parkinson?s disease and frontotemporal dementia. Neurofibrillary tangles (NFTs) composed of hyperphosphorylated and aggregated Tau protein are a major pathological hallmark of Alzheimer?s disease, as well as other neurodegenerative disorders collectively termed Tauopathies. Despite the strong clinical association, how wildtype human Tau proteins become hyperphosphorylated and cytotoxic remains poorly understood. Distinguished from other protein aggregates that cause dementia, overexpressing human Tau is well tolerated in the budding yeast with no apparent growth phenotype, even though human tau proteins are also hyperphosphorylated and aggregated in the yeast cells. Hence, no yeast genetic screen for Tau toxicity modifiers has been performed thus far. Yet, tremendous potential remains if Tau-induced cytotoxicity can be reproduced in the simple yeast model, permitting unbiased screens to uncover the molecular pathways involved in tau toxicity and its related diseases. In a preliminary screen, we have identified several ORF deletion mutations that show toxicity only when human wildtype Tau (2N4R) is expressed. Furthermore, two the mutant genes, THP1 and SAC3, belong to the TREX2 complex involved in activating stress response gene expression and mRNA export. Hence, we hypothesize that timely stress response at the transcription level is necessary for yeast cells to antagonize the toxicity induced by Tau overexpression. Especially related to the parental project of this application, altered cryptic transcription has been linked to transcriptional response to stresses. Hence, for this administrative supplement application, we will 1) validate the novel Tau toxicity model in mutant yeast cells by analyzing Tau phosphorylation and aggregation state; 2) investigate whether transcriptional regulation, especially cryptic transcription, is involved in Tau-induced toxicity in the thp1? and sac3? mutants. Successfully carrying out these aims will not only test whether transcriptional regulation is involved in Tau toxicity, but more importantly will establish a novel Tau toxicity model in the budding yeast, allowing future unbiased screens for genetic modifiers for Tau toxicity.